No effective vaccines yet exist for N. gonorroheae or for Group B N. meningitidis, the serogroup responsible for the majority of disease in the U.S. and Europe. Although meningococcal polysaccharide vaccines have been developed for some serogroups, immune response to thse vaccines in the age group most susceptible to disease (under two years) is poor. It is too early to be confident about pilus peptide vaccines being created for gonorrhea. Consequently, other antigens need to be identified if the goal of broadly protective immunoprophylaxis is to be achieved. Much of the evolutionary success of pathogenic Neisseria stems from surface antigenic heterogeneity that occurs among strains and even within a single strain. This project will examine immunoprophylactic potential of one of the very few conserved antigens in pathogenic Neisseria- the outer membrane protein-macromolecular complex (OMP-MC). Gonococcal OMP-MC is a surface-exposed, high molecular weight, disulfide-linked homopolymer of 10-12 76,000 d. subunits. Comparative peptide mapping and amino terminal amino acid sequencing show no differences among strains. Antisera to gonococcal OMP-MC from one strain bind to OMP-MC from all gonococcal and miningococcal strains tested. OMP-MC is immunogenic in disseminated gonococcal and miningococcal infections. Polyclonal and monoclonal antibodies to OMP-MC are bactericidal. To be attractive as a vaccine candidate, OMP-MC should be conserved, immunogenic in human infection, and elicit the production of antibodies that help the host prevent or overcome infection. Projected experiments will characterize the immune response to OMP-MC in serum, genital secretions, and spinal fluid from patients with genital, pelvic, or disseminated neisserial infections by solid phase radioimmunoassay. The extent of structural conservation of miningococcal OMP-MC will be assessed by limited proteolysis, isoelectric focusing of the subunits, and tryptic peptide mapping by high pressure liquid chromatography. Comparisons will be made to the known structure of gonococcal OMP-MC. Antibodies to OMP-MC will be tested for promotion of complement-mediated or phagocyte-associated bacterial killing. Selected antibodies will be tested for their ability to prevent meningococcemia in a well established mouse model. Protection by active immunization with OMP-MC will be assessed in this model. If protection is not achieved by antibodies to intact OMP-MC, peptide fragments shared among meningococci and gonococci will be tested in these assays. If protection is observed, the vaccine potential of OMP-MC for meningococcal and/or gonococcal diseases will be enhanced significantly.